Liquid ring pump control

ABSTRACT

A control system comprising: a suction line; an exhaust line; an operating liquid line; a liquid ring pump comprising a suction input coupled to the suction line, an exhaust output coupled to the exhaust line, and a liquid input coupled to the operating liquid line; one or more regulating devices configured to control flow of the operating liquid into the liquid ring pump; a first sensor configured to measure a first parameter of an exhaust fluid of the liquid ring pump; a second sensor configured to measure a second parameter of an operating liquid received by the liquid ring pump; and a controller operatively coupled to the sensors and the regulating device(s), and configured to control the regulating device(s) based on measurements by the sensors.

This application is a national stage entry under 35 U.S.C. § 371 ofInternational Application No. PCT/IB2019/052066, filed Mar. 14, 2019,which claims the benefit of GB Application 1804108.7, filed Mar. 14,2018. The entire contents of International Application No.PCT/IB2019/052066 and GB Application 1804108.7 are incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to the control of liquid ring pumps.

BACKGROUND

Liquid ring pumps are a known type of pump which are typicallycommercially used as vacuum pumps and as gas compressors. Liquid ringpumps typically include a housing with a chamber therein, a shaftextending into the chamber, an impeller mounted to the shaft, and adrive system such as a motor operably connected to the shaft to drivethe shaft. The impeller and shaft are positioned eccentrically withinthe chamber of the liquid ring pump.

In operation, the chamber is partially filled with an operating liquid(also known as a service liquid). When the drive system drives the shaftand the impeller, a liquid ring is formed on the inner wall of thechamber, thereby providing a seal that isolates individual volumesbetween adjacent impeller vanes. The impeller and shaft are positionedeccentrically to the liquid ring, which results in a cyclic variation ofthe volumes enclosed between adjacent vanes of the impeller and theliquid ring.

In a portion of the chamber where the liquid ring is further away fromthe shaft, there is a larger volume between adjacent impeller vaneswhich results in a smaller pressure therein. This allows the portionwhere the liquid ring is further away from the shaft to act as a gasintake zone. In a portion of the chamber where the liquid ring is closerto the shaft, there is a smaller volume between adjacent impeller vaneswhich results in a larger pressure therein. This allows the portionwhere the liquid ring is closer to the shaft to act as a gas dischargezone.

Examples of liquid ring pumps include single-stage liquid ring pumps andmulti-stage liquid ring pumps. Single-stage liquid ring pumps involvethe use of only a single chamber and impeller. Multi-stage liquid ringpumps (e.g. two-stage) involve the use of multiple chambers andimpellers connected in series.

SUMMARY OF THE INVENTION

The suction ability of a liquid ring vacuum pump can be influenced byadjusting the temperature of the operating liquid used in that liquidring pump. For example, at high vacuum levels, greater liquid ring pumpefficiency tends to be achieved by lowering the temperature of theoperating liquid. Conventionally, where water is used as the operatingliquid, the provision of lower temperature operating liquid is typicallyachieved by providing an open operating liquid circuit in which heatedoperating liquid from the liquid ring pump is expelled and replaced bycool, fresh operating liquid. Accordingly, liquid ring pumps can consumeconsiderable amounts of fresh water.

The present inventors have realised it is desirable to provide forcontrolling of operating liquid temperature and/or pressure of a liquidring pump in a way that minimises operating liquid and powerconsumption. Such control advantageously tends to reduce operating costsof the liquid ring pump.

The present inventors have further realised it is desirable to providefor controlling of a liquid ring pump in a way that prevents or opposescavitation in that liquid ring vacuum pump. Cavitation tends to be asignificant cause of wear and failure in certain liquid ring pumps,especially those operating at a low-pressure/high-vacuum condition. Suchcontrol advantageously tends to reduce or eliminate wear caused bycavitation.

In a first aspect, the present disclosure provides a control systemcomprising: a suction line; an exhaust line; an operating liquid line; aliquid ring pump comprising a suction input coupled to the suction line,an exhaust output coupled to the exhaust line, and a liquid inputcoupled to the operating liquid line; one or more regulating devicesconfigured to control flow of the operating liquid into the liquid ringpump; a first sensor configured to measure a first parameter, the firstparameter being a parameter of an exhaust fluid of the liquid ring pump;a second sensor configured to measure a second parameter, the secondparameter being a parameter of an operating liquid received by theliquid ring pump via the operating liquid line; and a controlleroperatively coupled to the first sensor, the second sensor, and the oneor more regulating devices, and configured to control the one or moreregulating devices based on sensor measurements of the first sensor andthe second sensor.

The one or more regulating devices may include a motor for a pump, oneor more valves, etc. The one or more regulating devices may beconfigured to modulate or regulate the flow of the operating liquid intothe liquid ring pump.

The controller may be coupled to the one or more regulating devices viaone or more variable frequency drives. The controller may control theone or more regulating devices via the one or more variable frequencydrives. For example, the controller may be coupled to each of the one ormore regulating devices via a respective variable frequency drive.

The first parameter may be a temperature. The second parameter may be atemperature. The controller may be configured to determine a function ofthe first and second parameters, and to control the one or moreregulating devices based on the determined function. The function maybe:

ΔT=T ₁ −T ₂

where T₁ is the first parameter and T₂ is the second parameter.

The one or more regulating devices may comprise a pump, which may becontrolled by a motor. The pump may be configured to pump the operatingliquid to the liquid ring pump via the operating liquid line. Thecontroller may be configured to determine an operating speed for thepump, and/or a motor that drives that pump, based on sensor measurementsof the first sensor and the second sensor. The controller may beconfigured to control the pump in accordance with the determinedoperating speed.

The controller may be selected from the group of controllers consistingof a proportional controller, an integral controller, a derivativecontroller, a proportional-integral controller, aproportional-integral-derivative controller, a proportional-derivativecontroller, and a fuzzy logic controller.

The control system may further comprise an operating liquid recyclingsystem configured to recycle operating liquid in the exhaust fluid ofthe liquid ring pump back into the liquid ring pump. The operatingliquid recycling system may comprise a separator configured to separateoperating liquid from the exhaust fluid of the liquid ring pump. Theoperating liquid recycling system may comprise a cooling meansconfigured to cool the recycled operating liquid prior to the recycledoperating liquid being received by the liquid ring pump.

The control system may further comprise a non-return valve disposed onthe suction line and configured to permit fluid flow into the liquidring pump and to oppose fluid flow out of the liquid ring pump. Thecontrol system may further comprise one or more spray nozzles disposedon the suction line and configured to receive operating fluid and tospray the received operating fluid into the suction line. For example,the one or more spray nozzles may be configured to receive operatingfluid via the operating liquid line.

The control system may further comprise a motor configured to drive theliquid ring pump. The control system may further comprise a third sensorconfigured to measure a third parameter, the third parameter being aparameter of a gas being received by the liquid ring pump via thesuction line. The controller may be further operatively coupled to thethird sensor, and configured to control the motor based on sensormeasurements of the first sensor and the third sensor.

In a further aspect, the present disclosure provides a control methodfor controlling a system. The system comprises: a suction line; anexhaust line; an operating liquid line; a liquid ring pump comprising asuction input coupled to the suction line, an exhaust output coupled tothe exhaust line, and a liquid input coupled to the operating liquidline; and one or more regulating devices configured to regulate flow ofthe operating liquid into the liquid ring pump. The method comprises:measuring, by a first sensor, a first parameter, the first parameterbeing a parameter of an exhaust fluid of the liquid ring pump;measuring, by a second sensor, a second parameter, the second parameterbeing a parameter of an operating liquid received by the liquid ringpump via the operating liquid line; and controlling, by a controlleroperatively coupled to the first sensor, the second sensor, and the oneor more regulating devices, based on sensor measurements of the firstsensor and the second sensor, the one or more regulating devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration (not to scale) showing a vacuumsystem.

FIG. 2 is a schematic illustration (not to scale) of a liquid ring pump.

FIG. 3 is a process flow chart showing certain steps of a first controlprocess implemented by the vacuum system.

FIG. 4 is a process flow chart showing certain steps of a second controlprocess implemented by the vacuum system.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration (not to scale) showing a vacuumsystem 2. The vacuum system 2 is coupled to a facility 4 such that, inoperation, the vacuum system 2 establishes a vacuum or low-pressureenvironment at the facility 4 by drawing gas (for example, air) from thefacility 4.

In this embodiment, the vacuum system 2 comprises a non-return valve 6,one or more spray nozzles 8, a liquid ring pump 10, a motor 12, aseparator 14, a pump system 16, a heat exchanger 18, a controller 20, afirst pressure sensor 22, a first temperature sensor 24, a secondpressure sensor 26, a first level sensor 28, a second level sensor 30,and a second temperature sensor 32.

The facility 4 is connected to an inlet of the liquid ring pump 10 via asuction or vacuum line or pipe 34.

The non-return valve 6 and the spray nozzle are disposed on the suctionline 34. The non-return valve 6 is disposed between the facility 4 andthe spray nozzle 8. The spray nozzle 8 is disposed between thenon-return valve 6 and the liquid ring pump 10.

The non-return valve 6 is configured to permit the flow of fluid (e.g. agas such as air) from the facility 4 to the liquid ring pump 10, and toprevent or oppose the flow of fluid in the reverse direction, i.e. fromthe liquid ring pump 10 to the facility 4.

The spray nozzle 8 is coupled to the heat exchanger 18 via a firstoperating liquid pipe 36. The spray nozzle 8 is configured to receive anoperating liquid (which in this embodiment is water) from the heatexchanger 18 via the first operating liquid pipe 36. The spray nozzle 8is configured to spray the operating liquid into the suction line 34such that the operating liquid is mixed with the fluid (e.g. a gas suchas air) in the suction line 34.

In this embodiment, the liquid ring pump 10 is a single-stage liquidring pump.

A gas inlet of the liquid ring pump 10 is connected to the suction line34. A gas outlet of the liquid ring pump 10 is connected to an exhaustline or pipe 38. The liquid ring pump 10 is coupled to the heatexchanger 18 via a second operating liquid pipe 40. The liquid ring pump10 is configured to receive the operating liquid from the heat exchanger18 via the second operating liquid pipe 40. The liquid ring pump 10 isdriven by the motor 12.

FIG. 2 is a schematic illustration (not to scale) of a cross section ofan example liquid ring pump 10. The remainder of the vacuum system 2will be described in more detail later below after a description of theliquid ring pump 10 shown in FIG. 2.

In this embodiment, the liquid ring pump 10 comprises a housing 100 thatdefines a substantially cylindrical chamber 102, a shaft 104 extendinginto the chamber 102, and an impeller 106 fixedly mounted to the shaft104. The gas inlet 108 of the liquid ring pump 10 (which is coupled tothe suction line 34) is fluidly connected to a gas intake of the chamber102. The gas outlet (not shown in FIG. 2) of the liquid ring pump 10 isfluidly connected to a gas output of the chamber 102.

During operation of the liquid ring pump 10, the operating liquid isreceived in the chamber 102 via the suction line 34 (from the spraynozzle 8) and via the second operating liquid pipe 40. Also, the shaft104 is rotated by the motor 12, thereby rotating the impeller 106 withinthe chamber 102. As the impeller 106 rotates, the operating liquid inthe chamber 102 (not shown in the Figures) is forced against the wallsof the chamber 102 thereby to form a liquid ring that seals and isolatesindividual volumes between adjacent impeller vanes. Also, gas (such asair) is drawn into the chamber 102 from the suction line 34 via the gasinlet 108 and the gas intake of the chamber 102. This gas flows into thevolumes formed between adjacent vanes of the impeller 106. The rotationof the impeller 106 compresses the gas contained within the volume as itis moved from the gas intake of the chamber 102 to the gas output of thechamber 102, where the compressed gas exits the chamber 102. Compressedgas exiting the chamber 102 then exits the liquid ring pump via the gasoutlet and the exhaust line 38.

Returning now to the description of FIG. 1, the exhaust line 38 iscoupled between the gas outlet of the liquid ring pump 10 and an inletof the separator 14. The separator 14 is connected to the liquid ringpump 10 via the exhaust line 38 such that exhaust fluid (i.e. compressedgas, which may include water droplets and/or vapour) is received by theseparator 14.

The separator 14 is configured to separate the exhaust fluid receivedfrom the liquid ring pump 10 into gas (e.g. air) and the operatingliquid. Thus, the separator 14 provides for recycling of the operatingliquid.

The gas separated from the received exhaust fluid is expelled from theseparator 14, and the vacuum system 2, via a system outlet pipe 42.

In this embodiment, the separator 14 comprises a further inlet 44 viawhich the separator 14 may receive a supply of additional, or “top-up”,operating liquid from an operating liquid source (not shown in theFigures). A first valve 46 is disposed along the further inlet 44. Thefirst valve 46 is configured to control the flow of the additionaloperating liquid into the separator 14 via the further inlet 44. Thefirst valve 46 may be a solenoid valve.

The separator 14 comprises three operating liquid outlets. A firstoperating liquid outlet of the separator 14 is coupled to the pumpsystem 16 via a second operating liquid pipe 48 such that operatingliquid may flow from the separator 14 to the pump system 16. A secondoperating liquid outlet of the separator 14 is coupled to an overflowpipe 50, which provides an outlet for excess operating liquid. A thirdoperating liquid outlet of the separator 14 is coupled to a drain orevacuation pipe 52, which provides a line via which the separator can bedrained of operating liquid. A second valve 54 is disposed along theevacuation pipe 52. The second valve 54 is configured to be in either anopen or closed state thereby to allow or prevent the flow of theoperating liquid out of the separator 14 via the evacuation pipe 52,respectively. The second valve 54 may be a solenoid valve.

The separator 14 further comprises a level indicator 56 which isconfigured to provide an indication of the amount of operating liquid inthe separator 14, e.g. to a human user of the vacuum system 2. The levelindicator 56 may include, for example, a transparent window throughwhich a user may view a liquid level within a liquid storage tank of theseparator 14.

In this embodiment, in addition to being coupled to the separator 14 viathe second operating liquid pipe 48, the pump system 16 is coupled tothe heat exchanger 18 via a third operating liquid pipe 58. The pumpsystem 16 comprises a pump (e.g. a centrifugal pump) and a motorconfigured to drive that pump. The pump system 16 is configured to pumpoperating liquid out of the separator 14 via the second operating liquidpipe 48, and to pump that operating liquid to the heat exchanger 18 viathe third operating liquid pipe 58.

The heat exchanger 18 is configured to receive relatively hot operatingliquid from the pump system 16, to cool that relatively hot operatingliquid to provide relatively cool operating liquid, and to output thatrelatively cool operating liquid.

In this embodiment, the heat exchanger 18 is configured to cool therelatively hot operating liquid flowing through the heat exchanger 18 bytransferring heat from that relatively hot operating liquid to a fluidcoolant also flowing through the heat exchanger 18. The operating liquidand the coolant are separated in the heat exchanger 18 by a solid wallvia which heat is transferred, thereby to prevent mixing of theoperating liquid with the coolant. The heat exchanger 18 receives thecoolant from a coolant source (not shown in the Figures) via a coolantinlet 60. The heat exchanger 18 expels coolant (to which heat has beentransferred) via a coolant outlet 62.

The heat exchanger 18 comprises an operating liquid outlet from whichthe cooled operating liquid flows (i.e. is pumped by the pump system16). The operating liquid outlet is coupled to a fourth operating liquidpipe 64. In this embodiment, the fourth operating liquid pipe 64 isconnected to the first and second operating liquid pipes 36, 40. Thus,the heat exchanger 18 is connected to the spray nozzle 8 via the fourthoperating liquid pipe 64 and the first operating liquid pipe 36 suchthat, in operation, the cooled operating liquid is pumped by the pumpsystem 16 from the heat exchanger 18 to the spray nozzle 8. Also, theheat exchanger 18 is connected to the liquid ring pump 10 via the fourthoperating liquid pipe 64 and the second operating liquid pipe 40 suchthat, in operation, the cooled operating liquid is pumped by the pumpsystem 16 from the heat exchanger 18 to the liquid ring pump 10.

The controller 20 may comprise one or more processors. In thisembodiment, the controller 20 comprises two variable frequency drives(VFD). One of the VFDs is configured to control the speed of the motor12. The other of the VFDs is configured to control the speed of themotor of the pump system 16. As described in more detail later belowwith reference to FIGS. 3 and 4, the controller 20 is configured toreceive sensor measurements from the sensors 22-32. The controller 20 isfurther configured to process some or all of these sensor measurements,and based on this sensor data processing control operation of the motor12 and the pump system 16, via the VFDs.

The controller 20 is connected to the motor 12 via a first of its VFDsand via a first connection 66 such that a control signal for controllingthe motor 12 may be sent from the controller 20 to the motor 12. Thefirst connection 66 may be any appropriate type of connection including,but not limited to, an electrical wire or an optical fibre, or awireless connection. The motor 12 is configured to operate in accordancewith the control signal received by it from the controller 20. Controlof the motor 12 by the controller 20 is described in more detail laterbelow with reference to FIG. 4.

The controller 20 is connected to the pump system 16 via a second of itsVFDs and via a second connection 68 such that a control signal forcontrolling the pump system 16 may be sent from the controller 20 to themotor of the pump system 16. The second connection 68 may be anyappropriate type of connection including, but not limited to, anelectrical wire or an optical fibre, or a wireless connection. The pumpsystem 16 is configured to operate in accordance with the control signalreceived by it from the controller 20. Control of the pump system 16 bythe controller 20 is described in more detail later below with referenceto FIG. 3.

The controller 20 is connected to the first valve 46 via a thirdconnection 70 such that a control signal for controlling the first valve46 may be sent from the controller 20 to the first valve 46. The thirdconnection 70 may be any appropriate type of connection including, butnot limited to, an electrical wire or an optical fibre, or a wirelessconnection. The first valve 46 is configured to switch between its openand closed state (thereby to allow or prevent the flow of the additionaloperating liquid into the separator 14, respectively) in accordance withthe control signal received by it from the controller 20.

The first pressure sensor 22 is coupled to the suction line 34 betweenthe facility 4 and the non-return valve 6. The first pressure sensor 22is configured to measure a pressure of the gas flowing in the suctionline 34, i.e. the pressure of the gas being pumped from the facility 4by the action of the liquid ring pump 10. The first pressure sensor 22may be any appropriate type of pressure sensor. The first pressuresensor 22 is connected to the controller 20 via a fourth connection 72such that the measurements taken by the first pressure sensor 22 aresent from the first pressure sensor 22 to the controller 20. The fourthconnection 72 may be any appropriate type of connection including, butnot limited to, an electrical wire or an optical fibre, or a wirelessconnection.

The first temperature sensor 24 is coupled to the exhaust line 38between the liquid ring pump 10 and the separator 14. The firsttemperature sensor 24 is configured to measure a temperature of theexhaust fluid of the liquid ring pump 10 flowing in the exhaust line 38,i.e. the temperature of the air and water mixture being pumped by theliquid ring pump 10 to the separator 14. The first temperature sensor 24may be any appropriate type of temperature sensor. The first temperaturesensor 24 is connected to the controller 20 via a fifth connection 74such that the measurements taken by the first temperature sensor 24 aresent from the first temperature sensor 24 to the controller 20. Thefifth connection 74 may be any appropriate type of connection including,but not limited to, an electrical wire or an optical fibre, or awireless connection.

The second pressure sensor 26 is coupled to the separator 14. The secondpressure sensor 26 is configured to measure a pressure of fluid withinthe separator 14. The second pressure sensor 26 may be any appropriatetype of pressure sensor, and may include a combined pressure sensor andswitch. The second pressure sensor 26 is connected to the controller 20via a sixth connection 76 such that the measurements taken by the secondpressure sensor 26 are sent from the second pressure sensor 26 to thecontroller 20. The sixth connection 76 may be any appropriate type ofconnection including, but not limited to, an electrical wire or anoptical fibre, or a wireless connection.

In some embodiments, the controller 20 is configured to controloperation of one or both of the motor 12 and the pump system 16 (e.g.via respective VFDs) based on measurements received from the secondpressure sensor 26. For example, if measurements received from thesecond pressure sensor 26 indicate that the pressure in the separator 14is too high (e.g. above a predetermined threshold value, such as 0.5bar(g)), the controller 20 may reduce the speed of or shut down one orboth of the motor 12 and the pump system 16. The controller 20 maydisplay a warning to a user of the vacuum system prior to controlling orshutting down one or both of the motor 12 and the pump system 16,thereby allowing the user to perform remedial action prior to thecontroller 20 acting.

The first level sensor 28 is coupled to the separator 14. The firstlevel sensor 28 is configured to detect or measure a level of theoperating liquid within the separator 14, e.g. within the storage tankof the separator 14. In particular, in this embodiment, the first levelsensor 28 is configured to detect when the operating liquid level withinthe separator 14 reaches a first level corresponding to maximum levelfor the separator 14. The first level sensor 28 is connected to thecontroller 20 via a seventh connection 78 such that, in the event thatthe operating liquid level within the separator 14 reaches the first(maximum) level, a corresponding signal or indication is sent from thefirst level sensor 28 to the controller 20. The seventh connection 78may be any appropriate type of connection including, but not limited to,an electrical wire or an optical fibre, or a wireless connection.

The second level sensor 30 is coupled to the separator 14. The secondlevel sensor 30 is configured to detect or measure a level the operatingliquid within the separator 14, e.g. within the storage tank of theseparator 14. In particular, in this embodiment, the second level sensor30 is configured to detect when the operating liquid level within theseparator 14 reaches a second level corresponding to minimum level forthe separator 14. The second level sensor 30 is connected to thecontroller 20 via an eighth connection 80 such that, in the event thatthe operating liquid level within the separator 14 reaches the second(minimum) level, a corresponding signal or indication is sent from thesecond level sensor 30 to the controller 20. The eighth connection 80may be any appropriate type of connection including, but not limited to,an electrical wire or an optical fibre, or a wireless connection.

In some embodiments, the controller 20 is configured to controloperation of the first valve 46 based on measurements received from thefirst and/or second level sensors 28, 30. For example, if measurementsreceived from the second level sensor 30 indicate that the operatingliquid level is at or below the minimum level, the controller 20 mayopen the first valve 46 thereby to allow additional operating liquid toflow into the separator 14. If measurements received from the secondlevel sensor 30 indicate that the operating liquid level is at or abovethe maximum level, the controller 20 may close the first valve 46thereby preventing additional operating liquid to flow into theseparator 14. In some embodiments, the controller 20 also controlsoperation of the second valve 54 via a communication link not shown inthe Figures. The controller 20 may control operation of the second valve54 based on measurements received from the first and/or second levelsensors 28, 30. For example, if measurements received from the firstlevel sensor 28 indicate that the operating liquid level is at or abovethe maximum level, the controller 20 may open the second valve 54thereby to allow operating liquid to drain out of the separator 14. Insome embodiments, the second valve 54 is a manual valve operated by auser.

The second temperature sensor 32 is coupled to the second operatingliquid pipe 40 between the heat exchanger 18 and the liquid ring pump10. The second temperature sensor 32 is configured to measure atemperature of the operating liquid flowing (i.e. being pumped by thepump system 16) into the liquid ring pump 10 via the second operatingliquid pipe 40. The second temperature sensor 32 may be any appropriatetype of temperature sensor. The second temperature sensor 32 isconnected to the controller 20 via a ninth connection 82 such that themeasurements taken by the second temperature sensor 32 are sent from thesecond temperature sensor 32 to the controller 20. The ninth connection82 may be any appropriate type of connection including, but not limitedto, an electrical wire or an optical fibre, or a wireless connection.

Thus, an embodiment of the vacuum system 2 is provided.

Apparatus, including the controller 20, for implementing the abovearrangement, and performing the method steps to be described laterbelow, may be provided by configuring or adapting any suitableapparatus, for example one or more computers or other processingapparatus or processors, and/or providing additional modules. Theapparatus may comprise a computer, a network of computers, or one ormore processors, for implementing instructions and using data, includinginstructions and data in the form of a computer program or plurality ofcomputer programs stored in or on a machine-readable storage medium suchas computer memory, a computer disk, ROM, PROM etc., or any combinationof these or other storage media.

Embodiments of control processes performable by the vacuum system 2 willnow be described with reference to FIGS. 3 and 4. It should be notedthat certain of the process steps depicted in the flowcharts of FIGS. 3and 4 and described below may be omitted or such process steps may beperformed in differing order to that presented below and shown in FIGS.3 and 4. Furthermore, although all the process steps have, forconvenience and ease of understanding, been depicted as discretetemporally-sequential steps, nevertheless some of the process steps mayin fact be performed simultaneously or at least overlapping to someextent temporally.

FIG. 3 is a process flow chart showing certain steps of an embodiment ofa first control process implemented by the vacuum system 2 in operation.

At step s2, the first temperature sensor 24 measures a first temperatureT1. The first temperature T1 is a temperature of the exhaust fluid ofthe liquid ring pump 10 flowing in the exhaust line 38, i.e. thetemperature of the air and water mixture being pumped by the liquid ringpump 10 to the separator 14. The first temperature T1 measurement issent by the first temperature sensor 24 to the controller 20 via thefifth connection 74.

At step s4, the second temperature sensor 32 measures a secondtemperature T2. The second temperature T2 is a temperature of theoperating liquid being received by the liquid ring pump 10 via thesecond operating liquid pipe 40. The second temperature T2 measurementis sent by the second temperature sensor 32 to the controller 20 via theninth connection 82.

At step s6, the controller 20 determines a temperature difference as thedifference between the measured first temperature T₁ and the measuredsecond temperature T₂. Thus, in this embodiment, the temperaturedifference ΔT is calculated as:

ΔT=T ₁ −T ₂

At step s8, the controller 20 acts to reduce or minimize the temperaturedifference ΔT by adjusting of a first control variable v₁(t).

In some embodiments, the controller 20 attempts to equalise thetemperature difference ΔT with a first threshold value, or to cause thetemperature difference ΔT to be within a first threshold range (e.g. afirst threshold value +/−a constant). The first threshold value may beany appropriate value, for example 1° C., 1.5° C., 2° C., 2.5° C., or 3°C. The first threshold value may be determined by testing, for exampleto determine a threshold value associated with high or optimum liquidring pump efficiency. The first threshold value may be dependent on asize or power of the liquid ring pump 10.

In this embodiment, the first control variable v1(t) is an operatingspeed of the motor of the pump system 16.

In this embodiment, the controller 20 is a proportional-integral (PI)controller. Thus, the controller 20 applies correction/adjustment to thefirst control variable v1(t) based on proportional and integral terms ofthe temperature difference ΔT. The adjusted value of the first controlvariable v1(t) may be determined as a weighted sum of the control terms(i.e. of the proportional and integral parameters determined by thecontroller 20).

In this embodiment, if the temperature difference ΔT is too high, forexample ΔT is above a threshold value such as the abovementioned firstthreshold value, the controller 20 increases the first control variablev₁(t). (Increasing the first control variable v₁(t) corresponds tospeeding up the pump system 16).

Similarly, if the temperature difference ΔT is too low, for example ΔTis below a threshold value such as the abovementioned first thresholdvalue, the controller 20 decreases the first control variable v₁(t).(Decreasing the first control variable v₁(t) corresponds to slowing downthe pump system 16.)

At step s10, the controller 20 controls (using a VFD) the pump system 16using the adjusted first control variable v1(t).

In particular, the controller 20 generates a control signal for themotor pump system 16 based on the adjusted first control variable v₁(t)determined at step s8. This control signal is then sent from thecontroller 20 to the pump system 16 via the second connection 68. Thepump system 16 operates in accordance with the received control signal.

Thus, in the event that the temperature difference ΔT is too high, thepump system 16 is sped up in accordance with the increased first controlvariable v1(t). Thus, the flow rate of relatively cool operating liquidinto the liquid ring pump 10 is increased. This tends to cause areduction in the first temperature T1 measured by the first temperaturesensor 24, thereby reducing the temperature difference ΔT.

Similarly, in the event that the temperature difference ΔT is too low,the pump system 16 is slowed down in accordance with the decreased firstcontrol variable v1(t). Thus, the flow rate of relatively cool operatingliquid into the liquid ring pump 10 is decreased. This tends to cause anincrease in the first temperature T1 measured by the first temperaturesensor 24, thereby increasing the temperature difference ΔT.

After step s10, the process of FIG. 3 repeats, for example until thevacuum system 2 is shutdown. The process of FIG. 3 may be performedcontinually, or more preferably continuously during operation of thevacuum system 2.

Thus, an embodiment of a first control process implemented by the vacuumsystem 2 is provided. The first control process comprises a control loopfeedback mechanism in which continuously modulated control of the pumpsystem 16 is performed.

Advantageously, the above described system and first control processallows for the control of operating liquid temperature in a liquid ringpump.

The above described system and first control process advantageouslytends to provide for improved performance and efficiency of the liquidring pump.

The above described system and first control process advantageouslytends to reduce the likelihood of overloading the liquid ring pump withoperating liquid. Furthermore, the likelihood and/or severity ofhydraulic shock (also called “water hammer”) tends to be reduced. Thistends to reduce damage to the liquid ring pump. Advantageously, theabove described system and first control process tends to providereduced or minimised operating liquid consumption. The operating liquidtends to be recycled in the above described system and first controlprocess. This tends to reduce operating costs of the liquid ring pump.

The above described system and first control process advantageouslytends to reduce the likelihood and/or severity of cavitation occurringin the liquid ring pump.

Advantageously, if the thermal load of the above described system islow, the pump system will tend to slow down. Thus, energy consumptiontends to be reduced.

The speed that the liquid ring pump 10 is running, i.e. the speed thatthe motor 12 drives the liquid ring pump 10, may be dependent on howclose the actual inlet pressure (i.e. the pressure in the suction line34) is to a target inlet pressure which may be defined by the facility4. Furthermore, the speed that the liquid ring pump 10 is running can belimited by the so-called “anti-cavitation control” process which willnow be described in more detail with reference to FIG. 4.

FIG. 4 is a process flow chart showing certain steps of an embodiment ofa second control process implemented by the vacuum system 2 inoperation. The process of FIG. 4 may be regarded as an “anti-cavitationcontrol” process.

At step s12, the first temperature sensor 24 measures a firsttemperature T₁. The first temperature T₁ is a temperature of the exhaustfluid of the liquid ring pump 10 flowing in the exhaust line 38, i.e.the temperature of the air and water mixture being pumped by the liquidring pump 10 to the separator 14. The first temperature T₁ measurementis sent by the first temperature sensor 24 to the controller 20 via thefifth connection 74.

At step s14, the controller 20 determines or estimates the vapourpressure of the operating liquid in the liquid ring pump 10 using themeasured first temperature T₁. In this embodiment, the operating liquidis water and, thus, the controller determines the vapour pressure ofwater for the first temperature T₁, which is hereafter referred to as“the water vapour pressure P_(wv)”. In this embodiment, the water vapourpressure P_(wv) is determined using an approximation formula, inparticular the Antoine equation. The water vapour pressure P_(wv) isdetermined as:

$P_{wv} = {A*10^{(\frac{m*T_{1}}{T_{1} + T_{n}})}}$

where: A is a constant value, for example, A may be between about 6.1and 6.2, e.g. A=6.116441;

-   -   m is a constant value, for example, m may be between about 7.5        and 7.6, e.g. m=7.591386;    -   T_(n) is a constant value (in Kelvin), for example, T_(n) may be        between about 240 and 241 Kelvin, e.g. T_(n)=240.7263 K; and    -   T₁ is the measured first temperature.

In some embodiments, one or more of the parameters A, m, and T_(n) mayhave different value to that given above.

At step s16, the controller 20 adds a so-called offset value to thedetermined water vapour pressure P_(wv), thereby to determine an updatedpressure value. Thus, in this embodiment the updated pressure value P isdetermined as:

P=P _(wv) +P _(offset)

where: P_(offset) is the offset value.

The offset value P_(offset) may be considered to be a safety margin. Theoffset value P_(offset) may be any appropriate value including but notlimited to a value between 1 mbar and 10 mbar, e.g. 1 mbar, 2 mbar, 3mbar, 4 mbar, 5 mbar, 6 mbar, 7 mbar, 8 mbar, 9 mbar, or 10 mbar. Insome embodiments, use of the offset value P_(offset) is omitted.

At step s18, the first pressure sensor 22 measures a first pressure P₁,the first pressure P₁ being the pressure of the gas flowing in thesuction line 34, i.e. the pressure P₁ of the gas being pumped from thefacility 4 by the action of the liquid ring pump 10. The first pressureP₁ measurement is sent by the first pressure sensor 22 to the controller20 via the fourth connection 72.

At step s20, the controller 20 compares the measured first pressure P₁to the determined updated pressure value P.

For example, the controller 20 determines an error value as thedifference between the measured first pressure P₁ and the determinedupdated pressure value P. Thus, the error value ΔP may be calculated as:

ΔP=P ₁ −P

At step s22, the controller 20 adjusts a second control variable v₂(t)based on the comparison performed at step s20. For example, thecontroller 20 may act to increase the error value ΔP by adjusting asecond control variable v₂(t).

In some embodiments, the controller 20 may adjust the second controlvariable v₂(t) if the error value ΔP is equal to a second thresholdvalue (e.g. if ΔP=0) or within a second threshold range (e.g. if ΔP≤0).The controller 20 may adjust the second control variable v₂(t) to causethe error value ΔP to increase.

In this embodiment, the second control variable v₂(t) is an operatingspeed of the motor 12. The controller 20 may adjust the second controlvariable v₂(t) to cause an increase in the error value ΔP by adjustingor varying the second control variable v₂(t) in a way that would cause adecrease in the operating speed of the motor 12. This reduction inoperating speed of the motor 12 would tend to cause the liquid ring pump10 to draw less gas from the facility 4 in a given time, which wouldtend to cause an increase in the pressure of the gas flowing in thesuction line 34, i.e. the first pressure P₁.

In this embodiment, the controller 20 is a proportional-integral (PI)controller. Thus, the controller 20 applies correction/adjustment to thesecond control variable v₂(t) based on proportional and integral terms,e.g., of the error value ΔP. The adjusted value of the second controlvariable v₂(t) may be determined as a weighted sum of the control terms(i.e. of the proportional and integral parameters determined by thecontroller 20).

In this embodiment, if the error value ΔP is too high, for example ΔP isabove a threshold value or above a desired threshold range such as theabovementioned second threshold value or range, the controller 20increases the second control variable v₂(t). (Increasing the secondcontrol variable v₂(t) corresponds to speeding up the motor 12 drivingthe liquid ring pump 10, which causes gas to be removed from thefacility 4 more quickly, thereby decreasing the first pressure P₁ of thegas flowing in the suction line 34.)

Similarly, if the error value ΔP is too low, for example ΔP is below athreshold value or below a desired threshold range such as theabovementioned second threshold value or range, the controller 20decreases the second control variable v₂(t). (Decreasing the secondcontrol variable v₂(t) corresponds to slowing down the motor 12 drivingthe liquid ring pump 10, which causes gas to be removed from thefacility 4 less quickly, which may result in an increase in the firstpressure P₁ of the gas flowing in the suction line 34.)

At step s24, the controller 20 controls the motor 12 using the adjustedsecond control variable v₂(t).

In particular, the controller 20 generates a control signal for themotor 12 based on the adjusted second control variable v₂(t) determinedat step s22. This control signal is then sent from the controller 20 tothe motor 12 via the first connection 66. The motor 12 operates inaccordance with the received control signal.

In the event that the error value ΔP is negative, the motor 12 is sloweddown in accordance with the decreased second control variable v₂(t).Thus, the operating speed of the liquid ring pump 10 is decreasedresulting in a decrease of the flow rate of gas through the suction line34 from the facility 4. This tends to cause an increase in the firstpressure P₁ measured by the first pressure sensor 22, thereby increasingthe error value ΔP.

Increasing the error value ΔP means that the difference between thefirst pressure P₁ and the water vapour pressure P_(wv) is increased. Inother words, the pressure of the gas received by the liquid ring pump ismoved away from the water vapour pressure P_(wv). This advantageouslytends to reduce the likelihood of the inlet gas causing cavitation inthe liquid ring pump 10.

After step s24, the process of FIG. 4 repeats, for example until thevacuum system 2 is shutdown. The process of FIG. 4 may be performedcontinually, or more preferably continuously during operation of thevacuum system 2.

Thus, an embodiment of a second control process implemented by thevacuum system 2 is provided. The second control process comprises acontrol loop feedback mechanism in which continuously modulated controlof the motor 12 is performed.

Advantageously, the above described system and second control processtends to allow for the control of fluid temperatures and pressureswithin a liquid ring pump.

The above described system and second control process advantageouslytends to provide for improved reliability of the liquid ring pump.

The above described system and second control process advantageouslytends to reduce the likelihood and/or severity of cavitation occurringin the liquid ring pump. For example, cavitation may be caused in theliquid ring pump by the inlet pressure (i.e. the pressure of gas fromthe suction line) being at or below the vapour pressure of the operatingliquid in the liquid ring pump. The above described second controlprocess advantageously tends to adjust the inlet pressure to move itaway from vapour pressure of the operating liquid, thereby reducing thelikelihood of cavitation. Thus, damage to the liquid ring pump caused bycavitation tends to be reduced or eliminated.

In the above described control processes, the liquid ring pump isoperated with variable speed drive (VSD). In other words, the controllercontrols the liquid ring pump to vary the speed at which the liquid ringpump pumps gas from the facility. When VSD is used, there may be a riskof the liquid ring pump shutting down if it is run at too low a speed.If the liquid ring pump was to shut down, gas from the chamber of theliquid ring pump may attempt to flow back from the chamber and out ofthe liquid ring pump to the facility. The non-return valveadvantageously tends to prevent or oppose this undesirable flow of gas,and is particularly beneficial for the liquid ring pump operated usingVSD.

Advantageously, the spray nozzle may be operated to vary the temperatureof the operating liquid entering the liquid ring pump.

In the above embodiments, the vacuum system comprises the elementsdescribed above with reference to FIG. 1. In particular, the vacuumsystem comprises the non-return valve, the spray nozzle, the liquid ringpump, the motor, the separator, the pump, the heat exchanger, thecontroller, the first and second pressure sensors, the first and secondtemperature sensors, and the first and second level sensors, and theconnections therebetween. However, in other embodiments the vacuumsystem comprises other elements instead of or in addition to thosedescribed above. Also, in other embodiments, some or all of the elementsof the vacuum system may be connected together in a differentappropriate way to that described above. For example, in someembodiments, one or more of the non-return valve, the spray nozzle, thepressure sensors, the temperature sensors, and the level sensors may beomitted. In some embodiments, multiple liquid ring pumps may beimplemented.

In the above embodiments, the heat exchanger cools the operating liquidflowing therethrough. However, in other embodiments other cooling meansare implemented to cool the operating liquid prior to it being receivedby the liquid ring pump, instead of or in addition to the heatexchanger.

In the above embodiments, a separator is implemented to recycle theoperating liquid back into the liquid ring pump. However, in otherembodiments a different type of recycling technique is implemented. Therecycling of the operating liquid advantageously tends to reduceoperating costs and water usage. Nevertheless, in some embodiments,recycling of the operating liquid is not performed. For example, thevacuum system may include an open loop operating liquid circulationsystem in which fresh operating liquid is supplied to the liquid ringpump, and expelled operating liquid may be discarded. Thus, theseparator may be omitted.

In the above embodiments, the liquid ring pump is a single-stage liquidring pump. However, in other embodiments the liquid ring pump is adifferent type of liquid ring pump, for example a multi-stage liquidring pump.

In the above embodiments, the operating liquid is water. However, inother embodiments, the operating liquid is a different type of operatingliquid.

In the above embodiments, the controller is a PI controller. However, inother embodiments, the controller is a different type of controller suchas a proportional (P) controller, an integral (I) controller, aderivative (D) controller, a proportional-derivative controller (PD)controller, a proportional-integral-derivative controller (PID)controller, or a fuzzy logic controller.

In the above embodiments, a single controller controls operation ofmultiple system elements (e.g. the motors). However, in otherembodiments multiple controllers may be used, each controlling arespective subset of the group of elements. For example, in someembodiments, each motor may have a respective dedicated controller.

In the above embodiments, the temperature difference is determined to beΔT=T₁−T₂. However, in other embodiments the temperature difference isdetermined in a different way, for example using a different appropriateformula. For example, the temperature difference may be a differentfunction of the first temperature T₁ and/or the second temperature T₂.For example, weights may be applied to the measured temperatures T₁ andT₂.

In the above embodiments, the Antoine equation is used to estimate thewater vapour pressure P_(wv) as

$P_{wv} = {A*{10^{(\frac{m*T_{1}}{T_{1} + T_{n}})}.}}$

However, in other embodiments, the water vapour pressure in a differentappropriate way, for example using a different approximation such as theAugust-Roche-Magnus (or Magnus-Tetens or Magnus) equation, the Tetensequation, the Buck equation, or the Goff-Gratch equation. In someembodiments, the water vapour pressure P_(wv) is determined as

${P_{wv} = {{2{0.3}86} - \frac{5132}{T_{1}}}}.$

In the above embodiments, the error value ΔP is determined to beΔP=P₁−P. However, in other embodiments the error value is determined ina different way, for example using a different appropriate formula. Forexample, the error value may be a different function of the firstpressure P₁ and/or the first temperature T₁. In some embodiments,weights may be applied to the measured pressure P₁ and/or the updatedpressure value P.

In the above embodiments, the pump is controlled to regulate or modulateflow of the operating liquid into the liquid ring pump. However, inother embodiments, one or more different type of regulating device isimplemented instead of or in addition to the pump, for example one ormore valves for controlling a flow of operating fluid. The controllermay be configured to control operation of the one or more regulatingdevices.

In the above embodiments, the second control process (described in moredetail above with reference to FIG. 4) is implemented to controloperation of the motor, and thereby the liquid ring pump. However, inother embodiments, this second control process is omitted, or adifferent process for controlling the motor and the liquid ring pump isimplemented instead.

1. A control system comprising: a suction line; an exhaust line; anoperating liquid line; a liquid ring pump comprising a suction inputcoupled to the suction line, an exhaust output coupled to the exhaustline, and a liquid input coupled to the operating liquid line; one ormore regulating devices configured to control flow of the operatingliquid into the liquid ring pump; a first sensor configured to measure afirst parameter, the first parameter being a parameter of an exhaustfluid of the liquid ring pump; a second sensor configured to measure asecond parameter, the second parameter being a parameter of an operatingliquid received by the liquid ring pump via the operating liquid line;and a controller operatively coupled to the first sensor, the secondsensor, and the one or more regulating devices, and configured tocontrol the one or more regulating devices based on sensor measurementsof the first sensor and the second sensor.
 2. The control systemaccording to claim 1, wherein the first parameter is a temperature. 3.The control system according to claim 1, wherein the second parameter isa temperature.
 4. The control system according to claim 3, wherein thefirst parameter is a temperature, and wherein the controller isconfigured to determine a function of the first and second parameters,and to control the one or more regulating devices based on thedetermined function.
 5. The control system according to claim 4, whereinthe function is:ΔT=T ₁ −T ₂ where T₁ is the first parameter and T₂ is the secondparameter.
 6. The control system according to claim 1, wherein the oneor more regulating devices comprise a pump configured to pump theoperating liquid to the liquid ring pump via the operating liquid line.7. The control system according to claim 6, wherein the controller isconfigured to determine an operating speed for the pump based on sensormeasurements of the first sensor and the second sensor, and to controlthe pump in accordance with the determined operating speed.
 8. Thecontrol system according to claim 1, wherein the controller is acontroller selected from the group of controllers consisting of aproportional controller, an integral controller, a derivativecontroller, a proportional-integral controller, aproportional-integral-derivative controller, a proportional-derivativecontroller, and a fuzzy logic controller.
 9. The control systemaccording to claim 1, further comprising an operating liquid recyclingsystem configured to recycle operating liquid in the exhaust fluid ofthe liquid ring pump back into the liquid ring pump.
 10. The controlsystem according to claim 9, wherein the operating liquid recyclingsystem comprises a separator configured to separate operating liquidfrom the exhaust fluid of the liquid ring pump.
 11. The control systemaccording to claim 9, wherein the operating liquid recycling systemcomprises a cooling means configured to cool the recycled operatingliquid prior to the recycled operating liquid being received by theliquid ring pump.
 12. The control system according to claim 1, furthercomprising a non-return valve disposed on the suction line andconfigured to permit fluid flow into the liquid ring pump and to opposefluid flow out of the liquid ring pump.
 13. The control system accordingto claim 1, further comprising a spray nozzle disposed on the suctionline and configured to receive operating fluid and to spray the receivedoperating fluid into the suction line.
 14. The control system accordingto claim 1, further comprising: a motor configured to drive the liquidring pump; and a third sensor configured to measure a third parameter,the third parameter being a parameter of a gas being received by theliquid ring pump via the suction line; wherein the controller is furtheroperatively coupled to the third sensor, and configured to control themotor based on sensor measurements of the first sensor and the thirdsensor.
 15. A control method for controlling a system, the systemcomprising: a suction line; an exhaust line; an operating liquid line; aliquid ring pump comprising a suction input coupled to the suction line,an exhaust output coupled to the exhaust line, and a liquid inputcoupled to the operating liquid line; and one or more regulating devicesconfigured to regulate flow of the operating liquid into the liquid ringpump; the method comprising: measuring, by a first sensor, a firstparameter, the first parameter being a parameter of an exhaust fluid ofthe liquid ring pump; measuring, by a second sensor, a second parameter,the second parameter being a parameter of an operating liquid receivedby the liquid ring pump via the operating liquid line; and controlling,by a controller operatively coupled to the first sensor, the secondsensor, and the one or more regulating devices, based on sensormeasurements of the first sensor and the second sensor, the one or moreregulating devices.